I can't really give a comment on this, since I haven't developed on a 8GB MBP. I think you should just expect a performance decrease once you're running your VM

I can't really give a comment on this, since I haven't developed on a 8GB MBP. I think you should just expect a performance decrease once you're running your VMs next to your development setup. If you run XCode with your iOS Simulator next to it, I don't think you'll notice a large performance difference.